Re"God bless you"

: I have a project due in school and my assignment is to find
out why we say "God Bless You" to someone after they sneeze. I can't
find any concrete info. Can anyone help?

GOD BLESS YOU -- "I wish you well. Samuel Johnson's (1709-84) last
words on his deathbed in 1784 were 'God bless you, my dear!' The
phrase is also used when someone sneezes, since in many cultures
it is believed that the soul leaves the body during a sneeze, and
God is called on to protect the sneezer from evil spirits at such
a vulnerable time. The word 'God' is often omitted." From "The Random House Dictionary of Popular Proverbs and Sayings" by Gregory Y.
Titelman (Random House, New York, 1996).